Problem: A group of adults and kids went to see a movie. Tickets cost $$6.50$ each for adults and $$3.00$ each for kids, and the group paid $$40.50$ in total. There were $4$ fewer adults than kids in the group. Find the number of adults and kids in the group.
Answer: Let $x$ equal the number of adults and $y$ equal the number of kids. The system of equations is then: ${6.5x+3y = 40.5}$ ${x = y-4}$ Solve for $x$ and $y$ using substitution. Since $x$ has already been solved for, substitute ${y-4}$ for $x$ in the first equation. ${6.5}{(y-4)}{+ 3y = 40.5}$ Simplify and solve for $y$ $ 6.5y-26 + 3y = 40.5 $ $ 9.5y-26 = 40.5 $ $ 9.5y = 66.5 $ $ y = \dfrac{66.5}{9.5} $ ${y = 7}$ Now that you know ${y = 7}$ , plug it back into ${x = y-4}$ to find $x$ ${x = }{(7)}{ - 4}$ ${x = 3}$ You can also plug ${y = 7}$ into ${6.5x+3y = 40.5}$ and get the same answer for $x$ ${6.5x + 3}{(7)}{= 40.5}$ ${x = 3}$ There were $3$ adults and $7$ kids.